“Current treatment options for OCD can cause side effects, including anxiety, insomnia, nausea and sexual dysfunction, and are not effective in all patients,” he said.

“This particular amino acid, N-acetyl cysteine (NAC), has anti-inflammatory and antioxidant properties and influences several neurochemicals within the brain.”

People with OCD often experience intrusive thoughts, such as a fear of germs or unwanted sexual thoughts, in addition to compulsive behaviours, including repetitive counting or checking, or excessive cleaning or hand washing.

OCD affects almost 500,000 Australians.

The National Health and Medical Research Council-funded trial underway in Brisbane, Sydney and Melbourne, aims to recruit 200 participants to take either NAC or a placebo over 24 weeks.

The trial is part of a wider collaboration between researchers from the Discipline of Psychiatry, University of Queensland; NICM Health Research Institute, Western Sydney University; and the Department of Psychiatry, The University of Melbourne.